With the Oct. 24 exit of Star Wars: Episode VII writer Michael Arndt, the studio is under the gun to keep the film on course for a 2015 release despite a script that several insiders say isn't close to ready.

According to those close to the project, producer Kathleen Kennedy and most of the film's creative team have asked Disney to push the release to 2016, but studio CEO Robert Iger is adamant that Episode VII -- perhaps the franchise's most anticipated installment since 1999's The Phantom Menace -- not budge. That has created enormous pressure on all involved, with director J.J. Abrams stepping in to take over scripting duties with Lawrence Kasdan, who co-wrote 1980's Episode V: The Empire Strikes Back, considered the best film in the series.

For his part, Arndt worked exclusively on Episode VII for most of the past year and already had penned a 40- to 50-page treatment before Lucasfilm was sold to Disney in October 2012. But as one of Hollywood's highest-paid screenwriters, who can command more than $300,000 a week doing rewrites, the Oscar-winning scribe (Little Miss Sunshine) was ready to move on to other projects.

Some sources say Abrams has become autocratic in recent months, wresting some casting control from Kennedy. But others disputed that notion, saying Abrams and Kennedy both have been involved in casting sessions. Unlike Kennedy, Abrams is said to be more in sync with Iger's desire to meet the 2015 release target -- which allows zero margin for error -- at all costs.

Although the 2015 schedule already is full of tentpoles including Disney/Marvel's Avengers: Age of Ultron, Warner Bros.' Superman-Batman mashup and Lionsgate's final Hunger Games, Iger has crafted a Star Wars game plan that hinges on Episode VII hitting the big screen that summer. The studio is expected to roll out Episodes VII, VIII and IX over a six-year period, with at least two spinoffs -- penned by a team including Kasdan and Simon Kinberg -- interspersed between.

Still, another project insider dismisses talk of problems and what the writer shuffle means for what is perhaps Hollywood's most valued franchise. "It's nothing out of the ordinary," says the insider. "Almost every big movie changes writers at some point. There's no drama here."